let arr = [5, 4, 3, "luck", 1, 2, "dog", 6, 9];
console.log(arr.join(''));// 543luck12dog69
console.log(arr.join());// 5,4,3,luck,1,2,dog,6,9
let arr1 = [
  {
    name: 'zg',
    age: 18
  },
  {
    name: 'kobe',
    age: 35
  },
  {
    name: 'lucy',
    age: 22
  },
];
console.log(arr1.join());
/**结果
[object Object],[object Object],[object Object]
*/
